Telephone subscriber&#39;s stepping switch



July 26, 1949.

c. MARBLE TELEPHONE SUBSCBIBERS STEPPING SWITCH Original Filed May 5, 1945 6 Sheets-Sheet 1 u M. -HOU m u All! L 0 3 K I1, u I l \E R G [I H 4 J J T/IIIIHLIIW m M N. F u H u T ffl H 2 H H w N H H H u B 3 r L MW w 0r \M M 3 WU rva-6l INVENTOR.

CLARENCE. MARBLE 2 A//////4//A/////////Z/Ill/I/l/l/iI/f/I??? a 2 a Z a a 3 .3 Z 9 9 Z a a A ZZZZZQZZZZ a g 9 a g Q a Q a g a a Q a Q a Q a g 9 a9 a a Q a a a Q Q Q g Q Q Q a g Q g a Q a a Q a a a a a a a Q a a a a g a a o; a a a Q Q Q Q a Q Q a Q g Q Q Q Q Q a a a a a a a a a a g a Q a g a a a a a a Z a a Q a a g a Q 9 Z a a ATTORNEY July 26, 1949. c. MARBLE 7 2,477,259

TELEPHONE SUBSCRIBERS STEPPING SWITCH Original Filed May 3, 1945 1 6 Sheets-Sheet 2- 584 585 see INVENTOR. CLARENCE MARBLE ATTORN EY Jilly 26, 1949. c, MARBLE 2,477,259

TELEPHONE SUBSCRIBERS STEPPING SWITCH Original Filed May 3, 1945 6 Sheets-Sheet 3 FIG. 10 911 24 972 910 962 953 934 932 925L358 FIG.I4

INVENTOR. CLARENCE MARBUE ATTOR N EY July 26, 1949. 2,477,259

TELEPHONE SUBSGRIBERS STEPPING SWITCH Original Filed May 3, 1945 6 Sheets-Sheet 4 D INVENTOR.

CLARENCE MARBLE ATTORNEY July 26, 1949. c. MARBLE TELEPHONE SUBSCRIBERS STEPPING SWITCH 6 Sheets-Sheet 5 Original Filed May 3, 1945 Q@ @9 6Q 9Q @Q FIG. l8

INVENTOR. CLARENCE MA RBLE %1 ATTORNEY July 26, 1949.

Original Filed May 5, 1945 C. MARBLE TELEPHONE SUBSCRIBERS STEPPING SWITCH 6 Sheets-Sheet 6 AT TORN E Y Patented July 26, 1949 UNITED TELEPHONE SUBSCRIBERS STEPPING SWITCH Clarence Marble, Middlesex, N. Y.

Original application May 3, 1945, Serial No.

591,703. Divided and this application January 16, 1948, Serial No. 2,727

7 Claims. 1

My invention relates to improvements in automatic switching systems for telephone and other communications equipment whereby a dial of the type now in common use in telephony is employed to activate receptive apparatus of a system in the selection, connection and control of its various elements, units or lines.

This application is a division of application, Ser. No. 591,703, filed May 3, 1945. This application is being divided out of the above mentioned parent application to specifically claim the specific structure of the automatic telephone switches used in this system while the system claims are being retained in the above mentioned parent application.

The objects of my invention are: first, to provide an automatic switching system which will employ a lesser number of operating elements, occupy less space, require less wire, require less maintenance labor and cost less than any other automatic switching system with an equal number of elements to be connected together and with the same operating features; second, to provide all of the operating features now in common use in the operation of automatic switching systems such as dial tone, reverting ringing tone, busy tone, a central source of power and automatic ringing; third, to provide selector equipment in which the dialing operations at calling telephone apparatus or similar pulsings established by other means, will, in one piece of apparatus, set up a circuit network so arranged that only a desired element, unit or line, of the system will respond; fourth, to provide in one piece of apparatus, individual to each element unit or line of the system, functions making this piece of apparatus responsive as the calling or as the called member according to its status in a connection; fifth, to provide equipment to which the calling and called members are attached for the duration of a connection and without interference with other connections; sixth, to provide equipment which will accompany the called member to its point of connection with the calling member and control the establishment of the connection; seventh,

'to provide equipment for the timing of connec- .ments, units or lines at the same instant and subsequent confliction; twelfth, to provide features which will permit two or more elements,

units or lines to employ the same call number T addition,

2 and respond accordingly as required for telephone private branch exchange trunks; thirteenth, to provide a talking circuit which is held clear of all operational equipment except the windings of the usual battery supply coils; fourteenth, to provide a grade of telephone linein this system adaptable to the various auxiliary circuits and apparatus normal to a major size telephone central oflice; fifteenth, to provide facilities for selective ringing on party lines.

Heretofore automatic switching systems have been used for the connection of telephone lines whereby a subscriber desiring a certain line could be connected by a sequence of operations thru limited channels, established by relays or switches in accordance with each dialing operation. To better explain, it is common practice in major size telephone oflices using switching systems now available, to direct incoming calls thru successive channels to desired thousands and hundreds groups then to the final unit associated with a desired line. With such systems, if the prescribed maximum load for the established channel had been met, subsequent calls directed into a channel when its maximum load has been attained are denied facilities and the call is lost or delayed. In any telephone system any group of lines, for instance, may have a high percentage of its lines in use, say 25%, yet the system as a whole may, at the same time and under maximum load, have but 3 to 5 percent of its lines in use. This invention establishes all lines in a system at the same status as part of one group consisting of the total number of lines in the system therefore apparatus need be provided only to meet the 3 to 5 percent of simultaneous connections or whatever percentage of connections average holding time and calling rate a given telephone system as a whole would warrant. In automatic systems heretofore have established a talking channel from the calling line thru a series of various equipments or relay combinations to the called line necessitating installation of equipment suificiently large to accommodate talking facilities together with selecting and control facilities throughout the system. With the present invention the called line is reached by a selector employing only signaling wires. To more clearly present this contrast, heretofore a system consisting of ten thousand terminations required a minimum of thirty thousand wires between switches or other apparatus used to select called lines and the called line equipment. With this invention but two hundred wires are required for the same purpose in a ten thousand line system. To further contrast the advantages of this invention with automatic systems heretofore developed it is pointed out that regardless of the size of the system, no train consisting of a plurality of selectors and connectors or large groups of relays is required to establish arconnection between the calling and called telephones of the system. When the calling line is activated it engages a selector which in turn activates and connects the called line to the calling line in accordance with the calling lines controlling operations.

This invention includes controls to prevent two or more incoming calls from arriving at the same instant and connecting simultaneously to the same selector equipment but other than that protective feature each call is established independently and is not effected by the calling operations of any other line. On completion of dialing a call might be delayed slightly awaiting connection or busy report but this delay would not be due to the action of any other line in'establishing its connection.

A clearer conception of the scope and purpose of the invention will be obtained from the following description taken in connection with the attached drawings in which:

Fig. 1 is a block diagram showing the relative arrangement of a small number of the principal elements of this invention, eight typical dial equipped telephones with their line equipments, their relation to multiple appearances of three selector circuits and their equipment, the scanning equipment, the selecting multiple and the various operating arms.

Fig. 2 is'an elevation view showing the arrangement f selector circuit contact lugs as multipled at each line. In this figure one side of twenty selector circuits are shown as they would appear at three line equipments.

Fig. 3 is a plan view of one side of the selector contact lugs as they would appear at three lines. It shows the arrangement of the contact lugs, assembly bolts, terminal lugs for connection of wire and the arrangement of supporting members.

Fig. 4 is an end view of the selector contact multiple and shows both of the selector circuit contact groups and their supports. The guides for line operating equipment are indicated and dotted lines represent the location of line apparatus in relation to the selector contacts.

- Fig. 5 is a schematic diagram of the line circuits and presents the electrical features employed by any line in either the calling or answering operations. Mechanical features essential in the description of the circuitfeatures are also presented. A dial telephone and ringing generator equipment are also shown to facilitate descriptions. Registration and alarm circuits are shown together with the tripping mechanism which activates them.

' Fig. 6 represents the appearance of two selector circuits and their contact lugs at a line equipment. Fig. Us a schematic diagram of circuit features to be added to the line circuits to control the sequence in which lines calling in at the same instant are accepted.

Fig. 8 is a schematic diagram of circuit features to be added to the line circuits where two or more .lines employ the same call number as in private operating arm of the line unit and is provided to more clearly present the operating and locking functions of the unit.

Fig. 12 is an isometric view showing the relative arrangement of contact fingers on one side of the line unit operating arm.

Fig. 13 is an isometric view showing the mechanism employed to activate an operating arm for propulsion by a continuously revolving eccentric wheel.

Fig. 14 is a schematic view showing the arrangement of the tripping mechanism employed to return the line units when their operating limit has been reached.

Fig. 15 is a schematic diagram of the selector circuits and includes representation ofsufiicient mechanical features to clarify its description.

Fig. 16 is a combined end view and partial section of the line pattern selector switch.

Fig. 17 is a plan view, in section, showing part of the operating mechanism of the line pattern selector switch.

Fig. 18 is a partial plan view showing the relative arrangement of contacts in the line pattern selector switch.

Fig. 19 is a partial end View and section of the hundreds and tens contact banks and show their relation to operating mechanism.

Fig. 20 is a plan view of a stamping which will provide the common contact springs for each horizontal row of selector pattern contacts.

Fig. 21 indicates wiring required between selectors and line equipments in a ten thousand line system using the principle illustrated in Fig. 22.

Fig. 22 is a functional diagram showing the essential features of the principle employed in establishing patterns for the selection of various lines in an eighty-one line system.

Fig. 23 is a schematic diagram of disconnect control features of the line equipment unit.

General description of this invention Any subscriber of a telephone system embodying this invention upon lifting the hand set or receiver of his dial telephone activates line equipment associated with, and individual to his line. This equipment consists principally of five relays, and an operating mechanism. Two of the five relays function when the line is calling and four of the five relays function when the line is being called (answering). The operating mechanism functions when the line is either calling or answering. The operating mechanism consists principally of a frame to which an arm carrying six finger-like contacts, or wipers, are attached. Its motion isimpelled by a ratcheting shaft which is activated by operation of certain relays and engagement with a continuously revolving eccentric or cam individual to each line equipment. The line equipment includes a holding mechanism consisting of a pin-like device which engages a slot in the movable arm on operation of a holding relay when required. Each line equipment also includes three condensers for battery supply control and reverting ringing tone; terminals not shown on the drawings for connection of the outside line extending to the subscriber's telephone and for connection of ringing current andv positive and negative battery; a tripping mechanism to reverse the direction of movement of the operating arm when used for calling or to sound an alarm as necessary when activated for answering. The six finger-like contacts, or wipers, carry three circuits. Two of the contacts carry the talking and pulsing circuit; two are activated.

use for a circuit which selects and holds idle selector equipment and the other two carry a circuit for connecting and holding the called line onto the selector circuit when the called line is As the operating arm of the line equipment progresses its contact fingers engage various stationary contacts or lugs arranged in groups of six. Three of these stationary contacts are in a tier on each side of the operating arm. Each of these groups of six stationary contacts or lugs comprise a multiple appearance of three two conductor circuits which extend to a selector. Each selector is represented at each line equipment of the system by a multiple appearance of the three circuits on lugs accessible for engagement with the operating arm of each line. One of the three circuits indicates idle or busy selector equipment and upon engagement with the operating arm of a calling line, if a certain selector circuit is idle, this circuit causes the line equipment operating arm on the calling line to lock in place. This circuit also changes status upon the connection of a calling line to selector equipment and indicates to subsequent searching calling lines that the selector circuit is busy. A relay in the selector circuit participates in establishing this busy condition and in holding the connection of the two circuits. Another of the three circuits is the talking path which terminates in the selector on battery and ground thru a battery supply relay. As the talking path is closed thru at the calling telephone the line apparatus is so arranged that the talking circuit is held open when crossing busy selector circuits to prevent clicks on such circuits. Although the calling line while searching for an idle selector circuit has battery across it at the same potential as that standing on the selector battery supply relay, differences in coil and circuit resistances might develop and result in clicks which the above feature guards against. With the connection of a calling line and an idle selector the battery supply relay of the calling line is disconnected from the connection and the calling station now-receives its battery supply from the selector. The engagement of a calling line and an idle selector caused the'holding mechanism of the calling line to function and the circuit engaging the operating mechanism of the line to open due to operation of a relay in the line circuit which looks up on finding an idle selector and remains locked up while a connection is established. This locked up relay also disconnects the battery supply relay from the line circuit, the calling line now receiving its battery supply from the selector to which it is attached. The third circuit into the selector is for use in connecting the answering-line to the calling line when the answering line has been found and activated by the selector.

During a period of peak load a calling line when searching for an idle selector may not find the desired circuit on its first movement across-the selector circuits. The line apparatus is so arranged that if a line unit completes an exploring trip across the selector circuits and does not find an idle selector it operates a tripping mechanism which causes the operating arm to'return to normal and again start searching for an idle selector. This procedure will continue until an idle selector is found or the calling party disconnects. As the line operating arms will only find it necessary to make two or more trips across the selector multiple during periods when all selector circuits are busy at one time it will only occur when the control the connection of called lines 6 traffic load has exceeded its anticipated normal peak so a register has been added to the system to indicate that an overload has occurred and its extent.

We now have the calling line connected to selector equipment and battery supply to the calling station established thru a relay in the selector. This relay operated when the connection between the calling line and the selector was established. Operation of this battery supply relay of the selector caused associated relays to operate. One of these associated relays being of a typedesigned for slow release is not afiected by dial pulsing so remains operated throughout the period of the connection and thereby keeps the other in its operated status. This second relay is responsible for many functions of the selector. When the selector was idle one of its back contacts presented ground to searching calling lines. When the selector is taken by a calling line it supplies battery to the relay controlling the locking mechanism of the calling line. This relay in the selector also controls establishment of dial tone and, if necessary, busy tone on the calling line together with connecting the equipment which will select the answering line when dialing takes place. It also releases the selecting equipment when the call is completed. I

When the sleeping equipment is taken into use by a calling line, dial tone is connected and indicates to the calling subscriber that dialing may be started. The calling subscriber operates his dial interrupting the current flowing in the line at a desired value according to the number of the desired telephone as controlled by the dial and causing an attendant series of breaks and makes to take place in the battery supply circuit which causes the battery supply relay to fluctuate accordingly. The selector circuit is so arranged that each series of pulsations causes certain contact banks, or; registers to operate in accordance with the dialing values. In a 10,000 termination exchange fourdialing operations would be required. Upon completion of these four dialing operations the selector equipment is so arranged that it stands ready for activation of the line being called. Coincident with completion of dialing by the calling line scanning apparatus is activated. The scanning feature is provided to and to prevent the simultaneous connection of two answering lines. This apparatus consists of an operating arm similar to that of the line equipment except that it carries but two contact fingers, or wipers, instead of six. Movement of the scanning arm is controlled. by an clectromagnet which causes its shaft to press against a roller which is in continuous motion. Finger-like contacts, or Wipers, on. the scanning arm engage contact lugs associated, with each selector circuit similar to. those at the line end of the sclector. When the contact fingers of the scanning equipment arrive at a line on which dialing has been completed it places battery and ground across circuits thru the selector register network and standing ready for operation on the answering relays of the line it is desired to call. The line circuit is so arranged that when its answering relays receive the momentary pulse of battery and ground from the scanning circuit the answering relays are disengaged from the selector network. The scanning pulse also caused the selector to complete its preparations for connection of the answering line by locking in place a contact which stabllshes a shortacross the third access I circuit. aiilic'ariiison the selector ircuit. lugs- Aesotiated with this locking contact is an additional contact which closes and causes an operating arm associated with the selector circuit to start functionin When the answerin relay of the called line disconnected themselves off of the selector register network one of the answerme relays. at the same time,started movement of the operating arm of that line by engagin its ratcheting shaft and the revolving eccentric individual to that the line. We now have the operating arm of the selector circuit and the operating arm of the line that the selector called, moving in unison. The contact lugs at the selector circuit are so arranged that the selector operating arm olosesa circuit thru a relay winding and the previously locked contact to the selector multiple at the line equipment. The operating arm of the called line having arrived at the selectors multiple circuit at the same time, the circuit partially established by the selector is completed thru the called line circuit where a hold relay and the locking mechanism of the answering line is operated and the called lines operating mechanism is caused to lock up. This completion of the circuit caused current to flow thru a winding of the'lock release relay of the selector and causes the locked contact to restore to normal thereby opening the contacts it had been holding in the closed position while waiting for the connection of the calledline. Opening of the contacts stopped the movement of the operating arm of the selectoncircuit by depriving its controlling relay of energy. The operating arm of the selector circuit then dropped back to its original position; If th called lines operating arm and the selectors operating arm had not arrived at the same selectors multiple in unison the selectors operating arm would have continued on to a local contact lug which would have established a circuit releasing the locked contacts and energizing an alarm circult.- An indicator would also have been activated to show maintenance forces which selector'circuit had failed to complete a connection. At the same time the operating arm of the called line having failed to keep iii-unison with the operating arm of the selector would be unable to connect so would have continued its movement until the operating limit had been reached at which time it'too would have operated an alarm and locked in place to indicate the lin introuble. If other selectors have completed dialing standing upon them the scanning arm will not return to normal but will meet each selector in turn, activate the line being called and the operating arm of the associated selector circuit. When the scanning'arm reaches its operating limit a tripping mechanism causes it to return-to its starting point. It is dead on this return movement as it is desirable to activate the answering lines in relatively the same sequence that the selector equipment was taken by the calling line. While one scanning arm is making its return movement to normal a second scanningarm can be started by the tripping action-of the-first scanning arm. This second. scanning arm has not been included in the detailed descriptions.

When the scanning apparatus places battery andground onto the circuit pattern, or register, established by dialing, the battery and ground are connected thru the answering line relays o the line unit of the called line if the line. is not busy. However, little called line is busy and the battery and ground are applied. by the scanning available.

mechanism the circuits. cancels. be c mpleted thru the answe ng l ne e ay but a circuit is completed thru a para el c rcuit the sel ctor network. parallel circui is mar inal and is unable to operate if the called line is found When the para lel circuit does. onc ate it locks up and maintains busy tone on the calling line until the calling party dis nnects- With operation of the hold relay of an answering line a circuit is closed thru a ringing relay in the line circuit and the called station is signaled by ringing its bell. This ringing circuit is that which is commonly used in telephone practice wherever'machine ringin is employed, in that an alternatin current is superimposed on a direct current. The called station when not in'use for talking maintains a condenser across its line al lowing the A. C. component to ring the hell but holding the circuit open to the D. component. When the called party answers, the direct cur.- rent is then allowed to flow and the ringing re.-

lay of the line circuit operates and remains oper ated while the connection is established. The called line receives its talking battery supply thru a relay in the line circuit. This relay normally stands across the line to activate the apparatus "when a call is incomin but when the line is an.-

swerin its status changes and it performs the battery supply function for the answering line.

' The main feature of this invention is the apparatus used for establishing the numerical value of the line being called and the projection of that value into the line equipments to activate the one line desired by the calling party. Each selector circuit consists primarily of such apparatus with attendant controls. In operating to a desired value in a ten thousand line telephone system but three relays are in use. Qne of these three relays closes contacts in accordance with the val.-

was. introduced when the calling party dials.

These'contacts are arranged in four banks, or registers, one being activated by the thousands dialing operation. another by the hundreds dialing operation, another by the tens dialing operation and the other by the units dialing operation. During each dialing operation a pulse absorbing relay is operatedwhich holds a circuit open until the pulsing of one dialing operation has been completed at which time it closes and activates the third relay which directs the next dialing 0r eration into its correct contact bank, Upon compl tion of theiour dialin operations one set of contacts in each of the four banks of contacts are closed and represent the numerical value determ ned b the dialing. Now let it be assumed that the desired line is numbered 3498. The ial.- lng operations. cl ed the third ere-up of con a ts in th thousa ds ban the fourth roup of contacts in the hundre s bank, he ninth group of contacts in the tens bank and the eighth group of contacts in the u its ank. The fi st two i ing operations selected the group of one hundred lines in which the desir d line is loca ed, n m y the fourth. hundred of the third thousand. A ten thousand line system can be divided into. one hundred groups of one hundred lines. In this invention thi is ac omp ished at h banks of ontacts. Each numeri al value of the ten n ts o the th sands bank is divided into ten un ts at the hundreds bank. When ny thou ands unit is activated it connects a common which stand acr ss t e u ts of the hundreds bank. In this case unit three of the housands bank was nersized thereby ener izing a c mmon representi the third thousand in the hundreds bank. The

fourth group of'contacts in the hundreds bank having been closed by the dialing operation we now have prepared a circuit to the group of one hundred lines in which the line we desire is lo 'cated. This circuit as now set up is a common to the one hundred line group selected We now have this circuit established on a common across the thousands bank of contacts on which the third setof contacts is closed projecting the circuit onto the third common across the hundreds bank on which the fourth set of contacts is closed therefore we have established a circuit to the group of one hundred lines desired Another circuit on which the selection is being made'enters the equipment at the common across the .tens group of contacts where the dialing had closed the ninth set of contacts which in turn is connected to the ninth common of the units bank where the eighth group of contacts being operated has completed the connection of the units side of the circuit to the ninety-eighth circuit of the hundred possible units selections. Now let it be assumed that this last circuit has been connected in multiple to the coils of all line equipment operating relays Whose call numbers end with the digits ninety-eight. In a ten thousand line system there will be one hundred of such relays connected to this circuit. The first circuit of the selector pair which, as has been explained, is common to the thirty-four hundred group of lines is connected in multiple to one side on each of the line equipment operating relays of that group. The selecting circuits have now been completed and are ready to be energized. Associted with the units bank of contacts is a contact which closes with the first units pulse and normally holds the selector circuits open when units dialing is not taking place. Also associated with the units bank of contacts is a set of contacts which control a pulse absorbing relay which keeps the selector circuits open until dialing has been completed thereby preventin premature operation which might result in a wrong number being connected. Upon starting ofthe units dialing the scanning apparatus is activated if not already in motion due to the action of another selector. A contact which closes with the starting of the units pulsing operations establishes a current thru the operating magnet of the scanning equipment thereby setting the scanning equipment in motion. The contact fingers, or wipers, of the scanning equipment carrying battery and ground engage a set of contact lugs associated with each selector circuit and on meeting a selector on which the dialing operations have been completed current passes thru the contact finger to which battery is connected, into a contact lug and over one of the selector circuits; thru a coil which controls a mechanically locked contact; thru the contact of the pulse absorbing relay; thru the ninth contacts of the tens group, the eighth contact of the units group on the ninth common and out to the lines ninety-eight of each hundreds group. The only-line ninety-eight which has the other selector circuit completed through the selectorregister to its associated line relay'is in the thirty-fourth hundred group of lines. This last mentioned selector circuit is connected thru contacts in the fourth group of contacts at the third common of the hundreds bank and thru the common and third contact of the thousands group to the. selectors scanning contactlug, a contact finger of the scanning arm and to ground. completing the circuit. When the above described current passed thru the answering relays of'line 3498 it caused these relays to operate thereby causing the operating arm of that line to start operation. One of these answerin relays locks itself energized and thereafter opens the selector register circuits extending to these answerin relays. At the same time the mechanically locking relay of the selector circuit, which was energized in series with the other of the answering relays of the line, closes a circuit thru the operating magnet of the selector circuits operating arm causing that arm to move in unison with the operating arm of line 3498. When the two operating arms arrive at their respective contacts in the selector circuit multiple the operating arm on line 3498 will lock in place and that line will now be connected to the proper calling line and to the selector circuit.

The four selector banks are restored to normal when the calling party disconnects and battery standing on a bank contact of the release relay of the selector is maintained in two electromagnets until the four groups of selecting contacts are normal at which time the restoring circuit is opened.

The answering line selector wires can be multiplied across as many banks of selector contacts as may be required by a given system.

Fig. 1 is a block diagram of the system and indicates in general the processes and equipment involved in establishing and maintaining a connection between two dial telephones using the automatic switching system with which this invention is concerned.

Each telephone is connected to the system thru line equipment individual to the telephone, This line equipment can be used for calling into the system or for answering purposes when the line is called. I e I The selector circuits place dial tone on the calling lines when such lines establish connection with aselector, select the called line when dialing takes place and control the connection be tween the calling and called lines.

The scanning circuit controls the sequence of establishin connections to prevent confiiction and is common to the system.

Referring to Fig. 1 assume a person at station A desires to call station G. He lifts the receiver or hand set of his telephone which energizes line equipment unit A--l. This line equipment unit is permanently associated with his line. The line operating arm M which is part of his line equip ment unit immediately starts moving upward 'to cross the connecting multiple in'search of an idle selector circuit. Selector circuit multiple contacts which appear at each line are indicated at Q. On finding an idle selector circuit, assume that it was J, the line operating arm M stops moving and is locked in place as shown at M-l in the diagram. With this connection between the callin line and the selector dial tone is established on the calling line and the calling subscriber at A on hearing it operates his dial to the directory number of the line he desires. The values dialed into the selector circuit J are set up on switches, or registers, in accordance with the. dialing operations. These switches establish circuits thru the selecting register network to the desired line but the circuits are not energized until the scanning operation takes place. The scanning equipment 0 is energized by the last dialing operation into a selector'or may already be in operation due to the action of some other selector. When contacts on the scannin arm P engage the selector circuit scanning contacts at S in moving across them, the operating arm of. the called line is activated, if dialing has been completed. Ihe circuits in the selector network standing on the-desired line equipment are energized and the hue equipment functions in its called or answering condition. The operating arm M of the desired station, in this case G, is activated and starts to move upward toward the connecting multiple. When the scanning arm P energized the circuit to the called line it simultaneously caused the selector operating arm N of selector circuit J to become energized and start to move upward toward the connecting multiple. The line operatingarm of equipment G I and the selector operating arm of equipment .J are now moving in unison and will reach the connecting multiple contacts Q of'selector circuit J at the same time; On doing so the line operating arm will lock in place and automatically ring the bell of the telephone at station G. The line operating arm M of line equipment A--l will remain on the selector circuit contact lugs Q until the call is completed or the callingparty disconnects. The selector circuit operating arm N falls back after having completed its iunction in escortin the called line to the correct circuit in the connecting multiple. p

The detailed descriptions to follow will cover many features not touchedupon in the foregoing brief outline. Busy indication, overload reg-istration, trouble indication, reverting ringing tone and ringing'control, together with other essential features will be presented with thedetailed descriptions of mechanical and electrical devices which are part of this invention. In addition, it

is believed that with this description and those to follow showing how connections can-boosted lished between exchange lines of the same grade it will be readily understood that other operating features normal to a major size telephone central office such as interoflice -trunks, information lines, service observing circuits; lines to operators pool tions, testing circuits, tool trunks, long lines, etc. can be incorporated into. this system without diiiiculty so it has not been deemed-essential to include descriptions and drawings of these and other normal features which have no influence -'on the design of the basic exchange :line switching system. Power supply sources and controls also have no influence in the design of this systemand where battery is indicated herein it may be assumed to be the usual 48'volt storage batterycom monly used in telephone central o-ffices. Where reference is made to ringing currenubusy t'oneor dial tone itmay be assumed that frequencies and 1' 1 and 13. Fla .9 is an elevation view showing that the unit is largely enclosed in a metal-supporting frame 9m and is installed by suspension from ironwork above; It can be seen that the removal or replacement of a line unit would be a relatively simple operation. Extendlng'acrossthe supportln'g frame 901 are two braces 93-1 and 913 which also serve as support "and guides for other equipment. Within the supporting frame 90! another rather complex frame is established. Its upper end consists of crosspiece 985 which carries con tact fingers, or wipers, 98-7, 989, 989, 992-, 993 and 994 Its sides are comprised principally of commutator strips L, 952, 953, 956, 951 and 958 and their insulation and supports. The bottom member of the frame consists of a strap which is provided to hold the frame rigid. In the center of this inner frame but not attached guide bar 940 is provided to keep the inner frame in alignment when it is raised and lowered. Ratchet bar 933 lifts the inner frame and-is enclosed in a guide channel 932; locking plate 934 functions in holding the inner frame at any desired level'w-hen ratcheted into position. Shaft 9 2l and its associated operating pawl 924 lift the inner frame causing its finger-like contacts to move across fixed contacts in the selector circuit connecting multiple illustrated in Figures 2, 3 and 4. At

each line equipment unit a continuously revolving eccentric wheel 995 is provided. When a line equipment unit is activated this eccentric S95 furnishes the necessary reciprocating motion for the ratcheting operations.

The lower end of ratcheting shaft 92 f carries two fittings, 9H which is attached permanently to shaft 921 by rivet 920, and 918 which a short shaft 919 which extends into fitting '9l'l. At the lower end of fitting SIB a wheel 909 is attached. This wheel 999 reduces friction as the irregularcontour of eccentric wheel 905 is lollowed by the ratcheting shaft assembly when in operation.

The top member of the inner frame is crosspiece 985 which appears in Fig. 9-. It is made or insulating material and carries two sets or three contact fingers, or wipers, one set attach end. 'Ihe contact fingers 981-, 988 and 989 are at one end and contact fingers 992-, 993 and 994 are at the other end. The two groups of contactnngers are held in place by grooved pieces of insulating material 986 and 99!. The grooves are provided on the lower side of ieces 986 and 991. as can be seen by reference to 1 2. These grooves hold the contact nngersin alignment. In Fig. 9 part'oi crosspiece 985 and part or piece 991 are shown broken awa to show a typical screw 969 and its insulating bushing 998. The screws holdmg pieces 9'86 and'99l in place are'the self threading type. Slight recesses are required in the sides of the contact finger material at the location or the screws. to allow the bushing and screw to be installed as shown. 'These recesses are not ii lustrated and can be omitted if the contact fingers and their associated selector circuit contact lugs in Fig. 2 are spaced sumciently far apart to clear the bushings. This however is undesirable as the over alllength of the installation of a number of line units will be increased considerably.

On the lerthand side of the supporting frame so! three electromagnets 501, 502 and 503 are mounted. These electromagnets when ener ized activate certain mechanical apparatus in addition to operating contacts involving electrical functions. Hereafter the electromagnets will be referred to as relays.

Relays!!! has its armature attached to a bar 1-396 shown in Fig. 13. This relay SM is energized when call is incoming. It also is energized while a called station is connected.

Relay 504 has its armature attached to a bar one which is arranged and equipped similar to the bar I386 of relay 50]. The bar 906 associate with relay SM is shown in Fig. 9 only.

The locations of the contact groups of relays 513-! and 504 are represented at Bill of Fig. 9. The contact group of relay =50! is shown in part at 98I and the contact group of relay SM is located immediately behind and parallel to the contact group 98I shown.

Bars 906 and I305 are normally in the same relative position and the apparatus they carry is identical except that their principal elements face inward toperrnit common engagement with cer= tain pieces of apparatus as will be explained.

Each of bars 906 and I396 is slightly larger at the contact end than at the relay end. Sliding pieces 9M and I3I4 are fitted over the small end of their respective bars 999 and I395 and held against the enlarged portion of the bars by springs 9I5 and I3I5. Each of the bars 906 and I305 carry a similar pin, though illustrated on bar I306 at I301 only. The sliding members 9M and I3I4 normally maintain a slight pressure on their respective springs (H5 and I3I5 due to the pressure of their respect ve contact springs 98! exceeding the pressure of springs 9I5 and I3I5. c

This margin of pressure is effective only when the respective relays 59I and 504 are deenergized.

The sliding members 9 I4 and I3 I 4 are so shaped that a lip or ridge I359 extends across their inner side. This ridge will press against latch 908 when bar 999 or I305 is shifted by operation of the associated relay. When a bar 999 or I396 is shifted toward the contact groups shown at 98! the sliding member 9l4 or I3 I4 on the bar will move with the bar due to the pressure of its springs 9I5 or l3I5, both of which are made of flat spring material and are suspended from the lower side of shelf 913. When the Sliding member reaches latch 908 the latch 998 will be moved in the di rection of fitting 9I8 until a lip at the lower end of latch 908 rests against fitting 9I8. The shifting of bar 909 or i396 also caused a pin in the re spective bar, illustrated as in bar I999 at I391 to move with the bar. This pin when shifted lifts latch 9I0 clear of notch 9II in fitting SIB. Latch 9I0 is made of flat spring material suspended from shelf 913 and normally maintains a slight pressure against fitting 9I3. wire spring material and. is also suspended from shelf 913 though the attachment is not illustrated. This spring BIS is so tensioned that it normally holds latch 908 clear of fitting 9 I 8.

When latch 9I0 is lifted clear of notch 9H tting 9E8 is free to move downward and is im-- pelled to do so by a wire spring 9 3. As previously-- stated, eccentric 905 is in constant rotation so the wheel 999 of fittin 9I8 will engage and fol low its contour when fitting 9 I 8 moves downward. At a low spot in the contour of eccentric 995 slot M2 in fitting 9I8 will have been carried downward to a point where it will engage the lip of' latch 908. When the lip of latch 998 enters slot 9I2 fittings 9I1 and 9I8 become coupled and ratchet shaft 92! is raised and lowered in a reciprocating motion as wheel 909 follows the vary ing contour of eccentric 995. This action con.- tinues while the coupling is maintained and the holding relay, to be explained later, is not operated.

Fig. 10 is a partial cross section of the line equipment unit at a point immediately below crosspiece 985. For clarity wires 995 have been omitted from this view. In Fig. 10 and in Fig. 11

holdin pawl 925 is shown adjacent to operating pawl 924. When ratchet shaft 92! moves upward operating pawl 924 which normally rests immediately below the upper tooth of ratchet bar 933 also moves upward and lifts ratchet bar 933. The upper end of ratchet bar 933 is in engagement with the lower side of crosspiece 985 therefore as Spring SIS is made ofratchet bar 933 lifts, the entire inner frame assembly is lifted accordingly. I

The reciprocating motion of operating pawl 924 and the holding action of pawl 925 in preventing reverse motion is an action in common use so a detailed explanation of slip, clearances, etc., will not be entered into. Operating pawl 924 is pivoted on pin 999 in-shaft SH and is held under slight tension against ratchet bar 933 by a wire spring 926 supported by a bracket which is part of brace 93!. Holdin pawl 925 is pivoted on the above mentioned bracket which is part of brace 93I and is held under slight tension against ratchet bar 933 by Wire spring 921.

The length of the teeth in ratchet bar 933 and the lifting distance in the contour of eccentric 995 are controlled by the ratchet bar slip and pawl clearance requirements and by the vertical dis tance between two similar terminal lugs in the selector circuit multiple which stands above the line units and is engaged by the contact fingers 981, 988, 989, 992, 993 and 994. If reference is made to Figures 2 and 4 it will be seen that while contact finger 981 is resting on a 202 contact lug,

. contact finger 988 is resting on a 203 contact lug,

contact finger 989 is resting on a 204 contact lug, contact finger 992 is resting on a 404 contact, contact finger 993 is resting on 405 contact lu and contact finger 994 is resting on a 406 contact lug. These six engagements represent connection of one line equipment to one selector equipment. To connect the same line equipment to the selector circuit imm diately above it is necessary to lift the contact fingers into engagement with similar numbered contacts appearing immediately above.

Each ratcheting cycle must provide this amount of lift on the upward movement to brin the com tact fingers into full engagement with a different selector circuit at each upward step.

Stop 922 has been inserted into shaft 92I to limit the downward movement of that shaft by engagement with the shelf of bracket 913.

The bottom of ratchet bar 933 contains a pin 931. When ratchet bar 933 is in its normal or lowered position this pin 931 extends thru a hole in a shelf which is part of brace 913 and engages contact group 998 holding its contacts under tension. When ratchet bar 933 is lifted the pin 931 raises with it and the contacts of group 939 function accordingly.

Reference to Fi ures 10 and 3.1 will disclose an L shaped piece of metal 934 which is part of the inner frame and is held in place b machine screws, the heads of which can be seen in Fig. 9 resting on pieces 959 and 995. This L-shaped piece is provided principally to support guide channel 932 which is welded in place, and to pro-- vide notches 995 which are used in the holding operations. These notches 935 are in the same number and the same spacing as the teeth in ratchet bar 933. The Lshaped piece 934 being part of the inner frame is raised and lowered with that assembly.

Associated with rela 592 is bar 929 which carries a sliding element 939 and a latch 929. The upper part of bar 923 is so arranged that it forms an arin-lilre projection which extends across the inner side of pawls 924 and 925. This arm can be seen more clearly in Fig. 11. associated with contact group 989 so when relay 592 is energized the contact group will function in its operated arrangement due to the armature of relay 992 shifting bar 923 slightly thereby applying pressure to the springs of contact group 989.

Bar 928 is also Bar .929 is slightly larger at its contact end than at its relay end. .At the relay end sliding member 939 rests against the end of the enlarged portion under the pressure of .spring 949. The pressure of spring 94.9 being less than that of contact group 989 the pressure of contact group 989 normally hold bar 928 in the position shown in Fig. 9 when relay 592 is de-energized. It will be noted that sliding member 938 is held clear :of L shaped piece 934 when bar 928 is normal. :Sliding member 939 has a lip or ridge on its inward side similar to that of sliding member i 314 shown in Fig. 13 at $359. When relay 592 is energized its armature causes bar 928 to shift toward contact group 989 thereby operating the contacts and at the same time causing sliding member 939 to move in the direction of the contacts 989 until its .lip rests against L -shaped piece 934 at which point :it will stop while bar 928 continues to move to its maximum.

The arm extending at a right angle from bar 928 and associated with pawls 924 and 925 causes these pawls to lift away from ratchet bar .933 against the pressure of springs 928 and 927 as bar 929 progresses. Latch 929, made of flat spring material and attached to bar 928 has a lip at the lower end which is pressed against ratchet shaft 92! where it engages notch 923 at the peak of an upward motion of shaft 92! thereby holding the ratcheting shaft assembly practically clear of eccentric wheel :985.

When pawls 924 and 92.5 are lifted clear of ratchet bar 933 this ratchet bar is no longer supported and therefore drops to its original position in guide channel .932 with its lower end resting on the shelf of brace 91 3 and its pin 93'! operating contact group 938.

Relay 592 is caused to operate by certain oircuits established by engagement of the contact fingers of the line unit and the contact lugs of the selectorcircuit multiple. This relay is re sponsible for holding a desired connection between a line unit and a selector circuit, therefore its operation is timed to take place immedi ately after a notch 935 in L-shaped piece 934 has passed the lip of sliding member 938 in an upward movement so that with the disengagement of pawls 9,24and 925 and a subsequent slight downward movement of the inner frame this lip will engage a notch 935 accordingly and hold the inner frame assembly in place throughout a connection.

When a call is completed and holding relay 592 is ale-energized and bar 92-8 resumes its normal position due to the pressure of contact springs the enlarged end of this bar being .in engagement with sliding member 999 cause it to disengage from the notch 935 in L-shaped piece 934. The pawls 924 and 925 resume their former position with their tips resting against ratchet bar 933 immediately underits upper tooth due to the shifting of the arm of bar 928 which had been holding them and due to the pressure of springs 926 and 927. The lip in latch 929 .disengages from the notch 923 in ratchet shaft 92! with the return to normal of bar 928 allowing the ratchet SZI to drop. I

When sliding member 9.30 on bar 928 disengages from a notch 935 in L-shaped piece 934 the entire inner frame of the line unit is without support therefore the whole assembly drops to its normal position where it rests on the top of ratchet bar 933 which had previously dropped when the locking operation by relay 5,02 took place.

16 Coil springs employed to impel the downward movement of ratchet bar 933 and the downward movement of the inner frame are not shown in theillustrations.

' When a line unit is employed in a calling-in operation its relay 59! is operated until the holding relay 592 is energized at which time relay 58| is ole-energized. When relay 5M is de-energized its bar i395 returns to normal, the lip .of

sliding member i3 it releases its pressure on latch 998 therefore its lip is caused to disengage from notch 5H2 due to the action of spring 955. At the same time pin I337 returned to its normal position releasing latch 9k? and allowing "it to return to a position where its lower end rests against fitting 958. When fitting 9H8 raises to its maximum due to the action of eccentric 95.5, latch 919 will fall into notch 9H thereby holding fitting Hi8 practically clear of eccentric 995. The

associated contact group also returns to its normal condition.

When a line unit is employed in an answering operation relay 594 is energized and remains operated until the call is released. Relay 59! also operates when the called station responds but its primary function in the answering circuit is to supply talking battery to the answering station. All of its ratchet control operations take place when relay 5M is energized in its answering function but they are not effective due to similar operations having been previously made by relay 599. However when the calling station disconnects relays 591 and 594 of the answeringline unit fall away together, bars 996 and i398 resume their normal positions; sliding members SM and HM release their pressure on latch .998 thereby disengaging it from notch 9H2, latch 918 engages notch 9i i due to the shifting of pins 1391 and 991. Pin 90? is not shown on the drawings.

Fitting 9E8 is locked up in a raised position once more.

A mechanism is provided to restore the inner frame to its normal position when the contact fingers of a line unit have traveled entirely across all of the .selector circuit multiple contact lugs in the calling-in operation. This mechanism also controls the locking up of the line equipment and the sounding of an alarm when a line unit fails to connect to its calling line during the answer- 0 ing operation of th line unit. For the purpose of this specification it is called the tripping mechanism and is illustrated principally in Figures .9

and 14 to which reference is now made. It will be seen that external springs of contact group 982 consist of fiat springs 94! and 948 which interlock at their upper terminals. Both springs are tensioned toward L-shaped piece 934 but do not quite touch it. The horizontal section .of spring 94'! is also tensioned upward so slightly. Near the bottom of L shaped piece 934 and on the side away from the guide channel 932, pin 945 projects toward the contact group 982 and is sufiiciently long to engage the bulge in spring 948 near its base. Vertically pin 945 is so located that when the contact fingers have crossed all of the selector circuit contact lugs a subsequent ratcheting operation will cause this pin 945 to travel over the bulge in spring 948 thereby pushing that spring toward the other springs of the contact group. This movement of spring 948 caused its upper end to move outward beyond a step in spring 941 which being tensioned upward causes the two springs to lock together. This movement of spring 948 also caused the contact springs to function in their operated status. While pin 945 was being lifted and was approaching and engaging the bulge in spring 948 pin 946 was moving away from its normal position in which it rests upon the end of spring 941. The operation of the contact springs 982 caused the upward movement of L-shaped piece 934 and the associated inner frame to stop and then return to its original position. Pin 946 upon reaching and engaging the tip of spring 941 pressed the end of that spring downwardsufiiciently to clear its step from engagement with spring 948 thereby causing thatfspring to return to its original status and the contact springs 982 to resume their non-operated status, 7

Spring assembly 982 is supported by a bracket 954 attached to the shelf formed by brace 913.

On each side of the frame assembly capped by cross piece 985 three thin strips of conducting material are mounted for use ascommutators in maintaining electric continuity to contact fingers 981,988,989, 992, 993 and 994 during the ratcheting operation and when thecontact fingers have arrivedata desired position. These commutator strips are numbered 951,952, 953, 956, 951 and 958 and are'shown inFiguresQ, 10 and 11. They are 'separated'by strips of insulation material 911 and faced by insulating strips 959 and 955. Machinescrews with insulating bushings hold the two assemblies together at taching them to L-shaped piece 934, a flat piece of metal 912, and crosspiece 998. Pieces 933, 912 and 998 are drilled and tapped to accommodate the machine screws. Each "commutator strip has a brush resting upon it under some tension. These brushes are shown in FiguresS, l and 11 and are numbered 969, 96!, 962, 965, 966 and 961 and are made of spring material. To hold the brushes in place on the commutator strips the ends are formed in the shape qfthe letter U. Mountings for the brushes are indicated at 919 and 915 of Figs. 9 and I0. 'Ihese mountings are arranged and held in place as are pieces 996 and 99l shown in Fig. i land described elsewhere. The lower end of each of the brushes is bent so as to project thru a slot in the line unit frame 99L The outward end of each brush is drilled for use as a terminal in attaching wire. The upper end of each commutator strip 95l, 952, 953, 956, 951 and959 is drilled for installation of wires 995 extending tothe contact fingers 981, 988, 989, 992, 993 and "994. These wires pass thru holes drilled in crosspiece 9'85 and thru apertures immediately 'above .the"'com'mutator stripsl I .y

Selector circuit nmltiple equipment In the preceding descriptions referenceshave been made to theQseIectOr circuit multiplecontact lugs the arrangement of whichis' illustrated principally in Figures 2, Sand 4.1 Figure 2 is an elevation view of one side of the selector circuit multiple as it will appear on the inwardside. Each line equipment of the system is associated with three vertical rows of contacts on each side of the selector circuit multiple. This, will be more clearly understood if reference is made to Figure 4 concurrently with Fig.2. Fig.'4 is an end view of the selector circuit multiple equipment in which the 29! bank of contactsand its-duplicate the 4H] bank ofcontacts form thetwo side walls of a corridor; At regular intervals, as indicated by 219, 2H and 2I2of Fig. 2, three vertical rows of contacts of each bank 29! are in alignment with. a etbiih Con c insersp a'l n -.1. n oth mr Qna-hali the.,. tac

fingers of each line unit, namely 981, 988 and 989 engage selector contactor lugs on one wall of the corridor and the other half of the contact fingers of the line unit, namely 992, 993 and 994 engage selector contact lugs on the other wall of the corridor. Figure 3 is a plan view of one-half of the selector circuit multiple contacts for a system employing but one pair of banks of selector circuit multiple contacts. With three vertical rows of contacts representing the longitudinal requirement for one line if a system exceeds, say 59 lines, the banks of selector contacts will be assembled accordingly in sections and the wiring tips of strips 292, 293 and 294 and their equivalents 494, 995 and 496 in the opposite bank will be duplicated at each end of the bank for installation of coupling wire between the sections. If sections of selector multiple contacts are used transpositions can be arranged in the coupling wiring between sections of th selector circuit multiple and in line circuit wiring to reduce the capacity effect in a long selector circuit multiple. It will be noted in Fig. 3 that the selector circuit multiple strips are narrowed considerably where material is not required for mounting screws, contact lugs and wiring terminals. This narrowing of the material in each selector circuit multiple strip to minimum width consistent with sturdy construction and low electrical resistanc also tends to reduce the capacity effect between selector circuit multiple strips. Typical mounting screws are shown in Figs. 3 and 4 at 392 and typical insulating bushings for the mounting screws 392 are shown at 3! in Fig. 4.

Straps 499 and 4M suspended from supporting ironwork 493 of the type commonly used in telephone buildings or cabinets hold the selector circuit multiple in place. These brackets 49! are drilled and tapped for attachment of angle irons 429 and 425 which are drilled and tapped at each .line equipment for attachment of supporting frames 99! of the line units and at each mounting screw 392 to hold the selector circuit multiple banks in place.

In Fig. 4, plates 492 cover the entire selector circuit multiple. They are drilled at each 392 screw for mounting purposes and at each line equipment unit to hold the 949 guide bar of each line unit in place.

By reference to Fig. 2 and Fig. 4 it can be seen that the selector circuit contact multiple 29! and its equivalent 4| 9 can be built up of successive layers of insulating material between selector circuit multiple contact strips 292, 293, 294, 494, 495 and 49B and with insulating strips at the top and bottom of the piles or its insulation can consist of moulded plastic material.

Electrical details ofthe line equipment unit In the foregoing description of the mechanical details of the line equipment unit it was found necessary, for clarity; to introduce some of its electricalfeatures. Now in describing the electrioal features it will be necessary to include some of the mechanical operations previously described. Fig. 5 presents, in schematic form the circuit of the lin equipment unit and includes sufficient mechanical details, also in schematic form, to show the relationship between mechanical and electrical functions.

' In describing the circuit operations of the line equipment unit it is necessary to introduce some of the features of a selector circuit so if reference is made to Figs. 5, 6 and 15 jointly a better 19 understanding of the operations will be obtained.

A single line equipment unit is employed for both the calling and answering operations of a line. In the calling operation certain circuits are established by the line equipment unit thru which the calling subscriber can, by dialing, connect his line to any desired line of the system. In the answering operation his line equipment unit responds to the calling operations directed into it by some other calling line.

A line equipment unit is provided for each station of a system. For example, on a four party line four line equipment units would be required for answering purposes. Three of the four equipments employed on a four-party line would have their calling features disconnected. Disconnection of th calling feature can be effected by opening two wires at the points indicated by reference 540 of Fig. 5 or by placing thin pieces of insulating material in break contacts 58I and will be bridged to the line at this point. Terminals at 5l8 of Fig. 5 are provided to connect the various ringing frequencies of generators 5|5 to the line equipment units in accordance with their party line ringing assignments.

Calling operations thru a line equipment unit Now let it be assumed that a callin operation is taking place from a station in a system embodying the apparatus with which this invention is concerned. To do so it is now necessary to refer to Fig. 5 which presents a typical line circuit. We will first assume that the telephone at 5I0 of Fig. 5 is being employed in the calling operation and that the receiver has been lifted.

For the purposes of this description the negative terminal of the central ofiice battery of the system will be referred to as battery and the positive terminal which is usually grounded in practice will be referred to as ground.

In Figure 5 the talking circuits are emphasized by heavy lines. Again referring to Fig. 5, at relay 50I battery and ground normally stand on the windings of that relay. A circuit from battery thru a break contact of contact group 982; thru a winding of calling relay 50!; thru a break contact 583 of locking relay 502; thru one side of an IDF jumper at 550, if an IDF is used; thru one side of the MDF or connecting rack jumper at 5II thru the telephone at 5| thru the other side of the MDF or connecting rack jumper at thru the other side of the IDF jumper at 550; thru a break contact 58I on looking relay 502; thru the other winding of calling relay 5e! and to ground. The completion of this circuit caused calling relay to operate and its bar I306 to function in starting the ratcheting operations described with the mechanical details of the line equipment unit shown in Figs. 9, 10, 11, 12, 13 and 14. The ratcheting operations lift the inner frame, which has been previously described and is easily identified by the reference numerals shown in Fig. 5, and each upward ratcheting step lifts the inner frame accordingly to engage contact fingers 981, 988, 989, 992, 903 and 994 with their respective 202, 203,

204, 404, 405 and 406 selector circuit multiple contacts of selector circuits. Two selector circuits and one appearance of their multiple contacts are shown in Fig. 6. The selector multiple contacts are represented by short heavy lines in Figs. 6 and 15. Relay 502 is a type designed for slow release so it will not fall down during the interval of dial pulse.

Now it is necessary to assume that the first selector circuit engaged by the calling line circuits contacts fingers was found to be idle. If reference is made to Fig. 15 it will be found that selector circuit multiple strip 406 is grounded on a break contact I582 of relay I503. When the wiper of contact finger 994 in Fig. 5 met the contact lug of selector circuit strip 406 in Fig. 6 a circuit was established from battery on the winding of locking relay 502 in Fig. 5; thru the winding of that relay to a break contact 577 on relay 504; make contact 596 of operated line relay 50l; thru brush 961; thru commutator strip 958; finger 994, selector circuit multiple strip 406 in Figs. 6 and 15; thru a break contact I582 of relay I503 and to ground thereby causing locking relay 502 of Fig. 5 to operate and perform its locking function by activating its bar 928 as described with the mechanical details of the line equipment unit.

We now have the contact fingers of the calling line standing on what had been an idle selector circuit. To prevent another calling line from connecting to the same selector circuit the following features are provided. With operation of locking relay 5020f Fig. 5 the calling line from station 5I0 which had been standing on open make contacts at relay 502 is now closed thru and the calling short of the station at 5I0 is established on contact fingers 981 and 988 thru brushes 960 and 96I and commutator bars I and 952 is now continued thru to relay I50I of Fig. 15 on selector circuit multiple strips 202 and 203 of Figs. 6 and 15. Battery and ground are standing on the windings of relay I50I thereby operating that relay thru the short established by operation of the switch hook 0f the telephone at 5I0 of Fig. 5. With the operation of relay I50I the groundmaintained on selector multiple strip 406 thru back contact I582 of relay I503 is removed due to operation of relay I50I placing battery thru the coil of relay I502 and a make contact on relay I502 placing battery thru the coil of relay I503.

When relay 502 of Fig. 5 operated it closed four make contacts and opened six break contacts. Two of the four make contacts closed the talking circuit thru to the selector circuit as previously described. The third make contact places ground on the ringing circuit which is standing on the winding of relay 505 but is now open at make contacts 512 on relay 504 therefore nonoperative in the calling line equipment unit. The fourth make contact 588 of relay 502 closes thru the ground standing on the winding of relay 502 and extends it through brush 956; thru commutator strip 951; thru contact finger 993; thru selector mutiple strip 405 of Figs, 6 and 15; thru a make contact I58I on relay I503 where it meets battery thereby holding relay 502 of Fig. 5 in the operated condition throughout the time that the calling short is maintained across relay I50I of Fig. 15 by the calling station at 5I0.

Two of the break contacts 58I and 583 of relay 502 are in the battery and groundcircuits thru the winding of relay 50I, and extending to the telephone at 5| 0. With the operation of relay 502 which has taken place this opening of the ing operations continue.

] battery and ground circuits thru the winding of re1ay'50I causes that relay to fall back and the -ratcheting operations of theline equipment unit to discontinue.

With the operation ofrelay 502 the locking and pawl'lifting actions of bar 928 in the line equipment unit also took place and the inner frame of the line equipment-unit re- ;mains in engagement with the selector circuit it had found except that ratchet bar 933 being no longer supported has fallen back to where its pin 931 opens the contacts of group 936 which had operated with the first ratcheting operation.

It will be noted that calling relay 50I of'Fig. 5

' operated two break contacts and two make contacts when energized. It also will be noted'that calling relay 50I was energized while a calling line was searching for an idle selector circuit. One

of the break contacts 59I of calling relay 50I opens a circuit to battery thru the winding of locking relay 502, brush 962, contact finger 989, selector mutiple contact strip 204 of Figs. 6' and 15- and'to answering control contact I520 of Fig. :15. ''When a line equipment is functioning as an answering line there is a short interval when 'contacts I520 and I52! are connected and ground is established on the'control contact I520, therefore to prevent false operation of relay 502,

shouldit engage a selector circuit during the *sho'rt-interval that ground is standing on the conductor under discussion the conductor is held open in line equipments when performing their callingfunction. I

The other break contact 590 associated with relay 50I of Fig. 5 opens conductor 539 in the answerin line pattern circuit of that particular line so that if the line is called while calling, a

busy signal will result. When holding relay 502 operates and calling relay 50I is de-energized the other answering line pattern circuit is held open by break contact 585 on relay 502. A complete description of the busy test feature will be found elsewhere in this specification. The make contact 593 of calling relay 50I is in 1? a circuit shown entirely in Fig. 5 from battery on a winding of locking relay502, thru contacts 593 and 511 to a make contact in contact group 928; to a make contact in'contact group 982 and to ground thru register 503. "function to cause operation of register 503 only This circuit can when the contact fingers of a line equipment have crossed over all of the selector circuits of the system on a calling operation without findin an idle selector circuit When ratchet bar 933 is lifted by mechanical'operations following the operation of relay 50I in its calling function as pre-' viously described, pin 931 attached to ratchet bar 933 is lifted from engagement with contact group 938 causing that contact to close. The ratcheting operations also lift the entire inner frame so pin 946 at'the top is moved away from engagement with spring 941 and pin' 945 is mov- 'ing toward the bulge in spring 949 as the ratchet- Springs 94'! and 948 comprise the tripping mechanism previously described with the mechanical operations of the line equipment unit. When the contactfingers have passed over all of the selector circuits pin 945 is so located that it engages'lthe bulge of 'spring 948 on a subsequent ratcheting step'causing that spring to interlock with spring 941 and hold the contacts of group 982 in an operated 'p'osition w th two contacts closed and one opened. When the pair of contacts of group 982 associated with register 503 are closed register;503is energized together withholding relay 502i 1 Opu frame drops back to normal and pin 946 rests on and depresses the tip of spring 94? allowing spring 948 to snap back to its original position thereby opening two contacts of group 982and closing the other. The contact of group I 982 15 which opened when spring 948 locked with spring 941 out off the battery supply to relay 50I'thereby-suspending all ratcheting operations until the inner frame returned to normal and closed this contact in group 982. The calling subscriber still waiting causes relay 50I to again operate and the ratchetin operations to again lift the contact fingers across the selector circuits in search for an idle selector circuit. Register 503 is the type now in common use in telephone oflices for message registration. The readings on register 503 will indicate to those concerned the number of times line equipment crossed the selector circuits and failed to find an idle selector circuit. The registers 503 are installed common to a group of lines.

When relay I50i of Fig. 15 was operated due to the connection of a calling line, relay I50I caused the operations of relays I502 and I503 over obvious circuits. Dial tone standing on "conductor I561 is introduced into the receiver of 'the calling telephone thereby indicating to the calling subscriber that dialing to the call number of the line he desires may be started. Conductor I561 is cut off from dial tone generated by a 40 break contact I595 in contact group 1518 which is operated by ratchet bar I 643 which is to be explained later. Dial tone will be heard by the calling subscriber in the intervals between the -dialing operations but will not be heard when dialing has been completed and the calling subscriber is waiting for the called line to connect. When the called line is connected the calling subscriber will hear reverting ringing tone while he is waiting for the called line to answer. This -will be explained with the answering line operations thru a line equipment unit.

@Answering operations thru a line equipment um't "Assume that a calling subscribers line is conjjnectedto a selector and that he has completed the dialing operations to select a desired line and "that the line circuit of the line he is calling is similar to that of Fig. 5. Shortly after the dialcn ing. operations were completed ground was apj plied momentarilyto conductor 532 of Fig. 5 and at the same time battery was applied momen- .tarily to conductor 530 of Fig. 5. The means employed for selecting the desired line and the introduction of battery and ground will be de- 'f scribed with selector equipment and circuit elsewhere in this specification. Ground from scarrning switch wiper, I550 is extended thru thesele ctor network to conductor 532 and thru break contacts 514 and 585; and thru the winding of if elayf504 tobattery for operating relay 504 to "connect groundto relay 504. Battery is extended "from the wiper I'55I of the scannin switch thru thejoper'ated selector network, which has registered" th balled linej'to conductof'53o and lthence y.-way..- t nta.cts-- 51 thru. the windin elay .504tq ground atcontacts 5.19. Relay 5,0 energizes and. ,at contacts..5l5wcompletes a l flocking circuit thru its right. hand. .windingwhile -aIT/ contacts; 514 vopens the circuit.- torelay 5&4 Qwhich now deenergizes.

"F With the. operation of .relay 504. its. bar 056- in a ddition ,to operating contacts. of groupwlilil causes 7 the various ratchetin operationstostart d the innerframe ofth line equipment unit move upward accordingly.

The batterysupplied. on. conductor. 53 5, .of Fig.

5 foroperation of relay50 i. passes thiuthe'wind- 3' ing of -relay .I 5050f Fig.,l5 thereby operating; that frelay simultaneously with relay .504 ..of -11?ig.,5. RelayI-5Ii8 of Fig; 15; carries threa-make con- .tacts. 4513,. I 515;. and 5;1'9 -which.;are-mechani- TI fc'ally locked into their operated positions-when Ifiielay. I508is energized. :-?Ihe secontactsremain locked until relayyl509 becomes energizedand releases them.

' When; the calling line established connection withthe selector circuit at Fig;=-15, .;r-elay I503; becomes energized and battery thru its;makel,con- -.--t acts I588 has beenv standing-.on-make contact I5'I4 .of relay. I508. ;With theoperation,pt relay 1508 this battery is connected thru contacts .4539 M and the winding oi -relay I5I0 :to; ground thereby --sa g. ns relay J an s a in er tchetin operations of the selector circuits operating arm causing itscontact fingers 1535, I536. and I153! to 54 u w r o d n y- Sel ector mutiple .strip 504 is-connected1 to -the other lock up make contact 1513 of relay I508-so f wvith the-operation of relay; I508 selectonmutiple gstrip; 4045s connected to answering control contact I52I. thru-Inak contact 4513. relay I508, v

The mechanical structure of the operating arm of theselector vcircuit .is essentially that of .the line eguipmentunit therefore 'it isebelievednnnecessary to provide a .second;des,c ription- .of the details .of all of its features. I Iowever, the-variations between the unit as employed in connection with a line; and as employed im-connection with a; selector -will be pointedout.

.Shaft, sens. continuous betweenv the line equipmentunitsancl the selector equipments. Ateach of thejline equipments it carrieseeecntric535and at each of-the selector. equipments it arries-a duplicate of. the905 eccentrics;showr n jig.

at I523. Shaft'002 and its ,associatedeccentric wheels at both equipmentsare in constant rotation. The lifts ofthe eccentrics 905 and-I523 are in alignment. This alignment is important G as the .operatingarmpr inner frame of the line equipment unit .of the line called. bythe selector ,equipment must risein unison with the operating I armor inner frame of the lector.-equipment. When the contact fingers 889 and 902 of. the called lineequipment unit of,F.ig. -5..engage their respective selector multiple. strips.,204 and 005,0! Fig, 6..contact fingers I535 and I536 of.F!ig.- 15 shouldat the same time be..in engagementwith V their respective answering. control..contacts.,l.52 0

,and. IEZI-Whieh are wired in series ;With;.$818 0t0l' multiple contact strip204, ,a make contact I513 ,on lockup relay [508a ,winding .relay I509.;a.nd

selector multiple contact strip. 404.

Relay-I5I0 of'Fig. 1,5 and its associatedbar I523 are-duplicates of calling relay I of, Ei g.- 5 and itsassociated bar I306. All-of the ratcheting functions of relay 50I are duplicated by -relay I 5I 0. Wheel I5ll l-of Fig.15 i-s a duplicate of wheel 909 of Fig. 5. The ratchet-shaft-assemi .bl com r r nci l ffi nei I Bast-letha I ,and:pawls..924.,and .9 25. .of Fig. 5 ,are. duplicated by 4527,4523, I 53L and .1532 ,of Fig-.15.: Ratchet ;-bar.-.0 33 of Fig. 5 is duplicated bysl5r30of Fig.;l5.

Commutatorstrip958 of Fig. 5 is. duplicated by I539 of Fig. .15. Contact finger -989-.of--Fig.- 5.:is

' duplicatedby-contact finger I536 of Fig-.15. The

location of. contact. finger 992 of Fig. 5..is.-duplioated by contact finger I536 but this contactfingerQis thesamel length ascontact finger .1535. .Contact finger I531 isin the location-of contact finger 5.84 andits length is also that of-contact finger I535. Contact; fingers 1.1535; and 1:536. are

a connected together instead; of =.being;wired to vcommutator strips as are thecontact fingers-of the lineequipment units as shown in Fig.- 5.

Relay; I.5I2 and its bar 1533 of the-selector e equipment of 'Eig;- 15- operate a contact land: lift the line equipmentrunit of Fig; 5. -:Howe,ver:r.elay

I.5I2 -does not perform a holding function. When -.relay I512 operates; ratchet-bar 15.30 returns .to ,normal dueltothe lifting ofpawls I53I= and I532 .and is-aecompanied-by-the inner framexof .the .iselector equipment.

Answering control contacts 15,20 and :I-5-2I;-are

. .the-same generalitypel and 3 construction as those of the selectorcircuitmultiple shown in Figs; .2; 3

and 4 except that a space appears between them q and wiring terminals are-required on-each. They are placed 'at the same level as the. 204selector -multiple strip of their respective selectorrcircuits and in vertical alignment withccontactrfingers 31535-and I536 oftheir respective: selector-equipments.

;-I-mmediatelyabove :the. level of :thellDDen answering control contacts 1520 and. .I52I.--and-'in 4 alignment with-contact finger .1531 a contact/ lug -I,522.-is installed aspart of a -circuitwvhich'indicates the failure of a selector and'an. answering line to establish: a -connectionvwiththez'calling :line. -The operationof :this circuit-will be. ex-

plained later.

Relay; 504; of Fig. 5; and relay 1 5 (hot "Fig. 15

having been operated iniunisonitheir respective associatedcontact :fingers move 1 upward :in unison. yWhen: contact fingers-989 and%:992 engage :selector circuit multiple strips. 2-04 and 404 ofthe selector circuit thev calling line is waiting on, and

- thruw-hich the answeringlline-was activated; the

:I.535;,and- ,I536-contact1fingers of-"Fig: 15 area-in engagement with 5 answering-control contacts I520 and I52I of that selector circuit.

,A circuit "is now established' in Figs.-5and115 from ground thru ,thewindingof rielayg 502; break contacts:.581Tithllhhfllfih 965;; t mcommutator Y strip; 956 .thrucontact finger 992 thru selector 4' circuit multiple -stripc404 ;,th-rua windingof relay I509;:thru,a lock-up.-;make contact I513 of: relay contact zfingers I536 and: I535; thru answering control contact I520; thru selector circuitrmulti- I508; thru; answering-.control contact-452 I ;=-thru ple strip 204;. thru contact finger 089; thru. commake contact; I552. When. relay 502 was 'oper- .atedits bar .926=caused-.all of the mechanical locking functions ofits associated lineequipment un-it top erate and-ratchetbar 933 to :drop back to norinal. The release of relay I508 opened contacts I519 to release relay I5 I so that the eccentric I523 no longer actuates arm I529.

When relay 504 was operated ground on one of its windings was connected thru its make contacts 515 to a break contact 586 on relay 502 and to battery therefore relay 502 held relay 504 operated until relay 502 energized.

When the calling line established connection with the selector circuit, battery from closed make contact I502 on relay I503 was established on selector circuit multiple strip 405, thru contact finger 993 of the calling line equipment unit, thru its commutator strip 951; thru brush 966; thru make contact 580 of the calling lines looking relay 502; thru a winding of that relay and to ground. This circuit is now employed in holding the calling line into engagement with the selector circuit. When the answering lines contact fingers engaged the selector circuit-s multiple contacts and became locked in place the 895 contact .finger of the answering line equipment unit ,also engages contact multiple strip 405 upon which the above described circuit is standing,

therefore battery thru make contact I502 on *relay "I503 andvselector multiple strip 495 to the :..calling lines relay 502 also holds relay 504 of the answering line in operation by passing thru contact finger 993 of the answering line; thru its commutator strip 951; thru its brush 966; to the -olosedmake contact 515 on its relay 504 and thru a winding of that'relay to ground, thereby holding the answering line equipment into engage- "ment-until'the calling subscribed disconnects.

When answering relay 504 was energized it closed thru a circuit from the telephone I 0 associated with its line equipment unit to ringing control relay 505 on the contacts of which the talking circuit now stands open toward condensers which are now in engagement with selector circuit multiple strips 202 and 203 across which the calling telephone is standing.

-When locking relay 502 operates, make contacts 580 places aground on break contact 559 of ringing control relay 505. The connection of this ground provides a path from ringing generator 5I5, thru ringing interrupter 5I6; thru ringing resistance lamp 5l1;- thru terminals at 516; thru a winding of ringing control relay 505;

thru the break contacts 558 of relay 505; thru make contact 510 on relay 504; thru IDF terminals at 550; thru MDF terminals at 5I I; thru the line; thru the ringer of the telephone; thru the condenser of the telephone at 510; back over 'the line, thru the MDF terminals; thru the IDF -'terminals; thru make contact 512 on relay 504, 1 to the ground established on break contact 559 of relay 505 by operation of relay 502. Alternating current flowing over this path causes the bell of -lay 505 to thecalled telephone.

The condenser at the telephone 5I0 allows the alternating component of the ringing'cu'rrent to pass thru thebell while it holds the direct current componentopen. Ringing control relay 505 is the type in common telephone use designed for "non-operation on alternating current'and ope'r ation on direct current. The battery in series with the generator 5I5 has no effect as long as only bells are across the line but with the lifting of a receiver on the line a path is provided for the direct current thru relay 505 which responds and locks up thru its other winding and making contact 580 on holding relay 5232, holding the re- ,lay 505 operated until holding relay 502 is deenergized andremoves the ringing ground.

Condenser 560 allows a sufficient quantity of the ringing current to pass thru it onto the calling line to be heard by the calling subscriber as what might be called an echo thereby informing him that the line he called is being rung.

With operation of relay 505 the talking pair is now continued thru make contacts 558 and 559; thru condensers 508 and 509; thru make contacts 582 and 584 on looking relay 502; thru brushes 960 and 96l, thru commutator strips 95I and 952, thru contact fingers 881 and 988 with which it is connected to selector circuit multiple strips 202 and 263 on which the calling telephone is standing.

A pair of wires extend from the talking circuit to the windings of line relay 58H to provide the talking battery for the answering telephone at 5"). Calling relay SM is operated in conjunction with the operation of ringing control relay 505 but the ratchet control operations of its bar I306 have already been performed by the ratchet control bar 998 of relay 504.

The deenergization and release of relay 504 immediately after the energization of relay 504 at g contacts 519 opens conductor 530 to provide a 508- and 509 and the contact fingers 981 and 988 so busy signal in case the answering line is wanted by other calling lines. Thus an open circuit on a conductor such as conductor 530 designates a busy line to the selector, or register.

Make contact 516 on relay 584 controls an alarm circuit which operates an audible signal and locks the line equipment unit in place when 'in its answering operation it fails to connect to the selector circuit thru which it has been called. This alarm circuit is from battery on the winding of locking relay 502; thru make contact 516 on relay 504; thru a make contact in group 982 of the tripping mechanism; thru the winding of alarm relay 506 and to ground. A make contact on relay 506 completes a circuit from battery; thru the alarm bell and to ground thereby operating the bell. 7 When the above circuit was completed thru locking relay 562 that relay performed its previously described locking function. As the alarm circuit can only be completed thru the tripping mechanism when the line equipment unit has operated to its limit in crossing the selector multiple and pin 945 has engaged the bulge in spring 948 it will be evident to attendants which line equipment unit had failed to perform its answering function. The line equipment unit is restored to normal by manually pushing its sliding member 930 clear of a notch 935 in L-shaped piece 934 shown in Fig. 5 and allowing the line equipment unit to return to normal where pin 946 will engage spring 941 of the tripping mechanism, cause contact group 982 to return to normal and open the circuit to ground on relay 506 thereby causing the bell to stop ringing.

Another break contact 511 of answering relay 504 is in series with a make contact in group 938 which controls operation of a register each time the line equipment unit fails to find an idle selector circuit while a calling operation is taking "place. "Theoperation o-fthis circuit has been explained.

Electrical and mechanical details of the called Zineselector unit establishedwitlrthe calling telephone the selector M cir-cu'its multiple contact strips 202 and -203 participated in the closingof a path from battery thru a winding of relay I50aI =thru-the telephone, back-to the other-*windingof relay I-50I and to =fground thereby energizing-relay I50I-and causing it to operate. "The dial of thecalling-tele- -phon'e is in series-withthe circuit which operated relay 4 50 I'- i and normally maintains the circuit closed =However-when= the dial is operated it causes asuccession of breaksto occur in the circuit between relay I50| and the telephone in -accordanceiwiththe value dialed.v .Thereforezwhen dialing. takes placerelay; I 50I de-energized. and energized alternately thereby introducingthe dial .ipulsings into the selector circuit.

l :Batterysupply-relay ..I50.I. carries a make and a break contact. Themakecontact I55 I, closes battery thru;-the :winding of va slow release relay .4502 ;which, iwhenz. operated releases too. slowly it) he completely; dc: energized when a dial puls :hreak: causes the. makacontact, 011 relay; 150i; to :operr; momentarily vtherefore. the make contact 45.63 f relay- .I 5102.; remainscws d; while. the I d ing operations aretaking place-.1 The make conta t "15.63 of relay-15.02 losesa c rc it r m b Ate-Ty: to the. windin of relay I503 and.- too-pgrpund tl'iereby operating that relay and holding it;Oper- .iateduwl iile the calling ,telephone is. standing across: relay"; I50I.With-.the. ,receiver. oil of the .hook switch. I 7

Relay I503 performs many supervispry-iunc- .tions in the selector circuit. When normal, break contacts. I582 provided the ground. on selector multiplestrip 400 by which a calling line equip- .ment-unit finds an idleselector. fMake contact I502. providesthe batter-yonvselector multiple .strip..405 which is part of the. circuit holding the calling line equipment locked to the idle selector circuit it. had found. Make contact [588 also places battery on a make. contact of relayjI 508 which at this time is not operated? Thisrnake contact of relayllfl3 also places battery on Windings offrelays I500 and 'I5I4 thru which it stands on contact lug i522; It also, places battery on a make contact of relay I5I-3" which operates when a line is found busy and on the'make'contact =l 510 of relay 1 509 for subsequent extension into relay *I'5I2.

Make contact "I502 on relay l 503 places battery on a make contact controlled bybar -I 533-associatedwitlr relay J I 5 I 2 so that when-relay I5 I2 is once-operated it' willbe held in operationzwhile the calling line is ccnnectedfi--Thismake contact on relay I503 also placesbattery on a make con- :tact of urel-ay1il580 and on selector multiple strip 28 405 which holds relay 50g of -Fig; 5 in op eratioril -Another make contact I583 on relay 'I'503 transmits dial tone to the calling subsc'riberby connecting-dial tone standing on conducto'r l 561 to the ground-side oi the talking pairiminediately ahead of re1ay I50I and thru condenser I590.

Another make -contact 1 I581 on rela'y 4503 establishes busytcne on the calling line when requiredw Busy tone standing on conductor 150B thru a make contact I59! on busy test relay I'5I3 whichis W. de-energized is carried thru closed make contact I581 0f relay I503; thru' condenser i590 and to the ground side of the talkingpair on the same conductor used by dial tone.' Operation of relay I5I3 is controlled by a break contact-I5'I2 on relay I580. l

- A break contact- I585 on relay I503 functions "when relay I500 is tie-energized on completion of a call and controls the restoration of called line selector equipment to its normal status.

An additional make contact on relay 1503 is in series with a break contact on relay I50I and the, windings of relays; l504 and I505, therefore -when relay I50I falls back on the: lstdial pulsing circuit break, battery is supplied momentarily thru the clos ed break'contact i562-of relay I50I; thru the closed make contact I504 of relay I503 thru the winding of relay I504; thru the winding of relay 1505 and to ground thereb'y causing relays'I504 and I505 to operate for the duration of the breaka fter which relays" I50I, I504 and I505 return totheir original status' v -When relay-1500 operates. a Weighted spring forming part-of its contact is caused to vibrate in a raised position andnormally will not come to rest on the other spring of the contact untilsufficienttime has expired for another pulsing action to have taken=p1ace therefore if another pulsingoperatioadoesoccur a fraction. of a second -after'the; first onethe Weighted sprin is again lifted-and only re-engagesthe other contact when'anyseries of pulsings has been completed. The contact of relay: I504 is closdwhenever that relay isenergized or,de-energized for a period of time slightly longer than the interval what takes place when alpulsing operation occurs.

When relay I50l was'first operated. by connection of the calling lineitslbreaklcontact I562 operated ahead of the-contacts on.- relay I 508, therefore relays -|:504 had remained .not energized until the dial pulse-took place;- Thecontact of relay I504 has round standing.- on it. and.v extending to a make contactonrelay I503.-..which operated fol- .lowing the operation of.:relay,.-I50l therefore this circuit extends thru the winding otirelay 1 506 to battery and has operated thatzrelay Relay lfiflfi remains-operated until the first pulsing. operation occurs at whichltime-relay I504 is energi-zed and: itscontact..opens, causin relay I505 to fallback; Ass-relay. .1505 ,operates with relay I504 we now have the following mechanical -operati0ns completed.

series of;dial.:p.u1ses,.the.contact on;re1ay;I504 is opens-therefore with the first pulse, relay, I5 06 is de energized andits 5 armatureifiit. nd vtl $9ir 

